In view of the significant amplitude of noise generated by operating jet engines of aircraft, it is common to employ sound absorbing panels or liners such as for nacelle inlet cowls serving the engines to thereby reduce the magnitude of noise volume produced by the engines and released into the environment. Two common acoustic treatments now used on nacelle inlet cowls are either a perforate face sheet system or a linear liner system. The former comprises a perforate face sheet bonded to a honeycomb core structure which is attached to a solid backface sheet. The linear liner system comprises a woven wire mesh structure bonded to a perforate sheet which, in turn, is bonded to a honeycomb core structure. To complete the assembly, the honeycomb core structure is bonded to a solid backface sheet in the same manner as in the perforate face sheet system.
While the linear liner system produces superior sound absorption in comparison to the perforate face sheet system, a problem exists with the woven wire mesh structure of the linear liner system because the mesh structure is exposed to the exterior. Specifically, when mechanics work inside the inlet, or when certain foreign objects strike the liner, the exposed mesh skin is relatively easily susceptible to damage which, of course, must then be repaired to prevent ingestion of mesh structure into the engine. Conversely, the perforate face sheet system does not perform nearly as well acoustically, but its exposed perforate sheet surface withstands usual wear.
In view of the superior performance found in the linear liner structure, it is apparent that a need is present for a liner having sound absorbing qualities equal to such linear liner, except with durability qualities equal to those present in the perforate face sheet system. Accordingly, a primary object of the present invention is to provide an acoustic liner exhibiting such characteristics by incorporating both a mesh structure and a perforate sheet structure.
Another object of the present invention is to provide an acoustic liner wherein a perforate sheet is exposed to the exterior and wherein a mesh structure is disposed immediately below the perforate sheet.
Yet another object of the present invention is to provide an acoustic liner wherein the liner additionally includes a honeycomb core structure immediately beneath the mesh structure and a solid backface sheet immediately beneath the honeycomb core structure.
Still another object of the present invention is to provide an acoustic liner wherein the mesh structure and the backface sheet are bonded to opposing sides of the honeycomb core structure with adhesive chosen and applied to prevent wicking of the adhesive into the woven stainless steel mesh.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.